<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0"/>
    <title></title>
    <style>
        html,body{
            padding: 0;
            margin: 0;
        }
        html{
            height: 100%;
        }
        body{
            /*背景颜色是默认占满的  但是高度并没有占满*/
            background: red;
            height: 100%;
        }

        /*
            html,body{height:100%}定义全屏的页面
        */
    </style>
</head>
<body>

</body>
</html>